Re: waiting on a condition

[Martijn Sipkema]

On Wed, 2004-10-13 at 17:30, Peter W. Morreale wrote:
> Have you looked at the wait_event() family yet?       Adapting that 
> methodolgy might
> suit your needs.

wait_event() seems to be what I was looking for; I don't really like the
condition being an argument.

> I don't know much about preemption yet, however I suspect it would be a 
> bug to allow
> preemption while the spinlock was held.  In other words, you might need 
> to do something like
> 
> disable preemption
> spinlock
> rc = condition
> spin_unlock
> enable preemption
> if (rc)
> ...
> 
> In other words, perform the test on the condition outside of the 
> critical region protected by the spin lock.

Well, that wasn't what I meant exactly. I was looking for a standard
way to wait on a condition so that it would still work when spinlocks
are converted to mutexes such as these new RT patches seem to do;
wait_event() seens to provide this, although I like to POSIX mutex/cond
semantics better.


--ms


P.S. I seem to have been removed from the LKML right after posting
my question (it was the last message I received). Is there something
terribly stupid I may have done? Was the question _that_ stupid?



> -PWM
> 
> 
> Martijn Sipkema wrote:
> 
> >L.S.
> >
> >I'd like to do something similar as can be done using a POSIX condition
> >variable in the kernel, i.e. wait for some condition to become true. The
> >pthread_cond_wait() function allows atomically unlocking a mutex and
> >waiting on a condition. I think I should do something like:
> >(the condition is updated from an interrupt handler)
> >
> >disable interrupts
> >acquire spinlock
> >if condition not satisfied
> >    add task to wait queue
> >    set task to sleep
> >release spinlock
> >restore interrupts
> >schedule
> >
> >Now, this will only work with preemption disabled within the critical
> >section. How would something like this be done whith preemption
> >enabled?
> >
> >
> >--ms
> >
> >
> >
> >
> >-
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> >  
> >

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